Device and method for controlling bulk density of dehydrated foodstuffs



Feb. 10, 1970 Filed Dec. 14, 1967 J. l. WADSWORTH ET AL 3,494,050 DEVICE AND METHOD FOR CONTROLLING BULK DENSITY 0F DEHYDRATED FOODSTUFFS 4 $heets-Sheet l MES I WADSWOR'IQHRS JA ALEXANDER S-GALLO GEOR gE-I M. ZIEGLER,JR. JAM J. SPADARO ATTORNEY 1970 J. l. WADSWORTH ET V DEVICE AND METHOD FOR CONTROLLING BULK DENSITY OF DEHYDRATED FOQDSTUFFS 4 Sheets-Sheet 2 Filed Dec. 14, 1967 INVENTORS JAMES I. WADSWORTH ALEXANDER S.GALLO GEORGE M. ZIEGLER,JR. JAMES J. SPADARO FIGZ Feb. 10, 1970 .1. l. WADSWORTH ETAL 3,494,050

DEVICE AND METHOD FOR CONTROLLING BULK' DENSITY OF 'DEHYDRATED FOODSTUFFS Filed Dec. 14, 1967 4 Sheets-Sheet 5 FIGA INVENTORS JAMES I.WADSWORTH ALEXANDER s GALLO GEORGE M.ZIEGLER,JR. JAMES J. SPADARO ATTORNEY Feb. 10, 1970 J. I. WADSWORTH ETAL 3,494,050

DEVICE AND'METHOD FOR CONTROLLING BULK- DENSITY F DEHYDBATED FOODS'IUFFS Filed Dec. 14, 1967 4 Sheets-Sheet 4 I I I I I I I I I 40 l I INVENTORS JAMES I. WADSWORTH ALEXANDER S.GALLO GEORGE M.ZIEGLER JR. JAMES J.SPADARd ATTORNEY United States Patent U.S. Cl. 34-110 2 Claims ABSTRACT OF THE DISCLOSURE Bulk density of high-sugar-content dehydrated foodstuff is regulated by varying the thickness of the sheet of the said dehydrated foodstuff as it is being discharged from a drum dryer. The thickness of the said sheet is here varied upon varying the angle of attack of the doctor blade in respect to the drum surface of the drum dryer.

A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to a device and a method for controlling bulk density of dehydrated foodstuffs. More specifically, this invention relates to an improvement ov r existing methods of controlling bulk density of drum dried high sugar content foodstuffs during processing through the modification of machinery used in processing the said foodstufls. Still more specifically, this invention relates to a method and apparatus for controlling the bulk density of high sugar content foodstuffs during drum drying by regulating the angle of attack of the doctor blade relative to the surface of a dryer drum. This invention has been utilized successfully in the preparation of dehydrated foodstuffs, such as sweetpotato flakes, peach flakes, pumpkin pie mix, and others, wherein the dehydrated foodstuffs have been produced with various selected bulk densities.

The main object of this invention is to provide a method of controlling bulk density in the preparation of high sugar content drum dried foodstuffs.

A second object of this invention is to provide an improvement in food processing equipment which is used in drum drying of high sugar content foodstuffs such that the product bulk density can be controlled during drum drying.

A third object of this invention is to provide a device which allows variation of the angle of attack of the doctor blade to the dryer drum without disturbing the equilibrium of processing operations, wherein the line of contact between the doctor blade and the drum does not change relative to the drum axis in a fixed coordinate system.

A fourth object of this invention is to provide a device and method for continuously controlling the bulk density of the foodstuff being processed while the machinery is in full operation.

A fifth object of this invention is to provide a device which while allowing the variation of angle of attack of the doctor blade in respect to the surface of the dryer drum permits an indefinite quantity of settings for the pertinent angle of attach of the doctor blade.

A sixth object of this invention is to provide a device which permits the plurality of adjustments of the doctor blade in respect to the surface of the dryer drum to be applicable to at least the single drum, double drum, and

ice

twin-drum dryer arrangements which are well known to those skilled in the art.

For purposes of the instant invention the bulk density of a dehydrated food product may be defined as weight per unit volume of material in the aggregate. This differs from true density in that the volume measured is occupied by both the discrete particles and the void spaces between them.

A continuing problem in the manufacture of dehydrated food products is the variation in product bulk density during processing which can result in undesirable variation in package fill. For example, a processor is packaging his product on a volume basis, variation in bulk density can result in either an overweight package, which will reduce the processors margin of profit, or an underweight package, which does not conform with label specifications. If a processor is packaging his product on a weight basis, a high bulk density will result in a package appearing to be underfilled, which is undesirable from the sales appeal point of view, and a low bulk density will result in the volume of the product being greater than that of the package thereby preventing the processor from filling his package. For a successful operation, the product bulk density must be maintained within suitable limits. Whenever there is a variation in bulk density which exceeds these limits it is necessary to revert to costly blending operations or other additional processing steps to obtain a product with an acceptable bulk density.

The bulk density of processed food products varies not only with processing conditions but also with factors beyond the control of the processor, such as crop growing conditions, variety of the farm product being processed, soil conditions at the growing location, etc. This is especially a problem for drum drying foods containing a substantial amount of sugar. Even though the true density of the product remains fairly constant, large variations in bulk density result indirectly from differences in the composition of the raw materials being processed. This is due to a rufliing effect which occurs as the dry but hot thermoplastic material is scraped from the drum surface by the doctor blade resulting in a sheet of material discharging from the dryer which is many times thicker than the film of material adhering to the drum surface. The thickness of the sheet varies with the composition of the material being dried, and this variation in sheet thickness produces variation in bulk density.

For example, in the manufacture of dehydrated sweetpotato flakes a thin film of sweetpotato puree, which is applied to a steam heated drum dryer, is dehydrated to the desired moisture content in a partial revolution of the drum. The dried material is then scraped from the drum surface by a doctor blade and discharged from the dryer in the form of a continuous sheet.

As the sweetpotato solids are scraped from the drum surface by the doctor blade a continuous ruflied sheet, which is much thicker than the film of sweetpotato adhered to the drum surface, is formed. The ruffling effect is related to the sugar content of the sweetpotato which will vary for different varieties, different growing areas, different climatic conditions, diflferent harvesting times, and different curing processes. A higher sugar content causes more rufiiing which results in a thicker sheet.

Bulk density varies with sheet thickness because the flaking equipment is designed to break the dry sheet into flake-like particles which have a non-varying diameter size-distribution. The only variation in particle size is in the flake thickness, therefore the variations in bulk density are due to variations in sheet thickness which result from differences in the raw materials. The bulk density of dehydrated sweetpotato flakes can range from 10 to 45 pounds per cubic foot, and this can be attributed to the variety, time of harvesting, and the time that the sweetpotato has been in storage (see Spadaro et al. paper bearing title Instant Sweetpotato Flakes Processing Modifications Necessitated by Varietal Differences, which appears in Food Technology, vol. 21, (3A), which is a March 1967 issue). A processor, who normally will receive several different lots of sweetpotatoes in one day, will have a variation in the bulk density of his product. This will result in an undesirable variation in the packaging operation especially where filling is done on a volume basis.

In the prior art we find that several methods are currently used for controlling bulk density of drum dried high sugar content products; however, all of these methods have serious drawbacks. A brief discussion of these methods follows.

One method of controlling the bulk density is to change the particle size by varying grinding or flaking conditions. There are several disadvantages to doing this. First, the appearance of a dehydrated flaked product varies with variation in particle size distribution. This is undesirable from the sales standpoint since a processor wants to provide his customers with a product having uniform appearance. Secondly, the particle size of a dehydrated product affects its reconstitution properties. Too large a particle would reduce the rate of Water pickup, while too small a particle would either float to the top of the fluid or would tend to cake or form balled-up agglomerates. Excessive grinding, as would be required to obtain a substantial increase in bulk density, would cause an undesirable amount of fines which, after being packaged, tend to separate giving the impression of a nonuniform product.

Another method of controlling bulk density is to vary the thickness of the puree film adhered to the drum surface. This is one of the methods recommended by Lazar and Morgan (Instant Applesauce, Food Technology, vol. 20 (4), 531), but this has not proven successful. The production capacity of a drum dryer is closely related to the film thickness. Any variation in film thickness will result in variation of production rate which is extremely undesirable in continuous operation (see Wadsworth et al., Instant Sweetpotato Flakes-Factors Affecting Drying Rates on Double Drum Dryer, Food Technology, vol. 20 (6), June 1966).

A third method, one which is currently used commercially in the manufacture of dehydrated sweetpotato flakes to control bulk density, is to vary the composition of the material being fed to the drum dryer, such as adding sugar or enzymatically treating said material. There are two main disadvantages to this method. The first disadvantage is that there is a time lag (which in known cases has been timed at more than 60 minutes) between the corrective action of altering the composition of the material going to the dryer and the desired effects of changing the thickness of the sheet coming off the dryer. The second disadvantage here is that this is a trial-and-error procuredure because, currently, there are no simple tests which can be used to predict exactly what modification in the composition of the feed material is required, thus making control of bulk density very erratic. In addition, it may not be possible to vary the composition of the feed material due to the restrictions placed upon such materials by the buyer. For example, in the production of sweetpotato flakes purchased by the US. Quartermaster Corps, specifications prohibit the addition of sugar and take a view that this is an adulteration of a natural product.

US. Patent 3,009,815, granted to G. L. Lorant et al. in 1961 relates to the manufacture of strained food products which would have a relative high percentage of natural or added sugar. The novelty feature in his patent is a stretching of the hot plastic food sheet as it is being removed from the dryer thereby decreasing the sheet thickness. This method is also recommended by Lazar and Morgan for controlling bulk density of instant applesauce flakes. With Lorants method bulk density could be decreased within limits; however, it is not possible to increase the thickness of the sheet over that being discharged from the doctor blade.

The instant invention, in general, can be described as a two-faceted invention which relates to food processing, and consists of a method of controlling the bulk density of certain high sugar content foodstuffs during drum drying and an apparatus employing the said method. A selected bulk density can be obtained by adjusting the angle of attack of the doctor blade to the drum surface.

To illustrate the method and apparatus which comprise the instant invention atention is called to the drawings.

FIGURE 1 is a schematic side elevation view to present the location of the various angles.

FIGURE 2 is a side elevation view of the apparatus of the invention.

FIGURE 3 is auxiliary top view of the doctor blade assembly adjustment mechanism.

FIGURE 4 is a front elevation view, a schematic view of the assembled apparatus.

FIGURE 5 is a schematic front view of the adjusting support member.

FIGURE 6 is a schematic top view of the adjusting support member shown in FIGURE 5.

A schematic presentation of the more important aspects of the method of the instant invention are shown in FIGURE 1, and a more detailed explanation of the studies leading to this invention has been presented by these inventors in their paper Controlling Bulk Density of High Sugar Products During Drum Drying, which appeared in Food Technology, vol. 21, No. 7, pages 103, in July of 1967. From these studies it was concluded that angle a (FIGURE 1), which is the solid angle formed by the tangent to the drum surface and the beveled edge of the doctor blade, when held at a selected point about the periphery of the drum has an effect on the bulk density of the final product. Experience has provided those skilled in the art with the knowledge of the selecter point at which the doctor blade contacts the drum. The selected point is 34, on FIGURE 2 which is viewed as a line in FIGURE 4. Viewed from a side elevation, the edge of the doctor blade becomes a point. The optimum location of the doctor blade relative to the point of applying feed material to the drum surface depends upon the design of the dryer and the characteristics of the feed material and is immaterial in the discussion of our invention.

To illustrate the method employed in the instant invention reference is made to FIGURE 1. This drawing is a schematic presentation of the method of the invention. This side elevation auxiliary view shows the periph cry of the dryer drum 1 being touched by the doctor blade 2 at the point of contact 34, which is also the edge of the doctor blade 12. The fine line T is the edge of a surface tangent to the drum at line of contact 34. Three angles are shown. These are referred to as a, 'y, and [3, as shown in FIGURE 2. The angle which affects the bulk density of drum dried high sugar content materials is the solid angle oz, which is formed by the intersection of T, which is tangent to the surface of the drum at the line of contact 34 with surface B which is parallel to the beveled surface of the doctor blade. When the angle 0; (FIGURE 1) is increased the bulk density of drum dried high sugar content products is decreased, and when angle a is decreased the bulk density is increased. It should be noted that variation of angles 5 and 7 (FIGURE 1) do not affect the bulk density when angle on was held constant.

An explanation for the variation of bulk density with angle a can be deduced from physical reasoning. The temperature of the material on the drum approaches the temperature of the drum surface by the time it reaches the doctor blade. Foodstuffs having a high sugar content tend to be thermoplastic and tacky at the operating tempera tures of such machinery, even when the moisture content has been reduced to less than 4%. As the material is scraped from the drum surface by the doctor blade it ruffles to form a sheet discharging from the dryer which is much thicker than the film adhered to the drum surface. The bulk density, as stated previously, varies with the thickness of the sheet of food material.

The degree of ruffiing (i.e., thickness) of the formed foodstuff sheet for a particular product depends upon the amount of impedance to the movement of the dry food material across the beveled surface of the doctor blade. For example, the degree of ruffling can be temporarily reduced (yielding a thinner sheet) by coating the doctor blade with a fluorocarbon spray thereby lowering the coefficient of friction between the material and the doctor blade which reduces the resistance to the movement of the sheet of foodstuff. The variation of the angle a has a similar effect. Reducing a has the effect of increasing the impedance to the movement of the high sugar content material and increasing a lowers the impedance. For physical reasoning a rough analogy can be drawn with fluid flow through a pipe bend where an increasing deflection results in an increasing friction loss.

In Table I, the effects of change of doctor blade angle with respect to the surface of the drum (angle a) on the bulk density of three drum dried high sugar content food materials are shown. These results are for the edification of the reader, and must not be construed as limiting the invention in any manner whatever.

TABLE I.EFFECT F CONTACT ANGLE BETWEEN A DOCTOR BLADE AND THE SURFACE OF THE DRUM DRYER ON THE BULK DENSITY OF VARIOUS SE- LECTED DRUM DRIED HIGH SUGAR CONTENT FOOD PRODUCTS Bulk Density (pounds per cubic foot) Sweetpotato Peach Pumpkin Pie Angle (degrees), a Flakes Flakes Mix Reference is now made to the apparatus of the invention, an illustration of which is presented by FIGURES 2, 3 and 4. The invention is not intended to be limited by this illustration. All technical equivalents which operate in a similar manner to accomplish the same purpose as those shown in FIGURE 2 are meant to be included in this disclosure. In reference to FIGURE 2, specifically, the illustration describes a dryer drum 1, wherein the rotation of the drum as viewed would be clockwise and the material adhered to the drum surface would be scraped off by doctor blade 2, and discharged from the dryer in the form of a continuous sheet 23, which is supported by roller 24, and deposited into a suitable container 25. The doctor blade 2 is held against the blade bar 26 by gib plate 27. This, together with yoke 5, which is welded to he blade bar 26 constitutes the blade holder assembly 3.

The doctor blade holder assembly 3 is pivotally held in place by holder adjusting support 4L in the bore 29L. Said adjusting support 4L is pivotally held to dryer frame 13, which is resting on dryer bed 14, by fulcrum bolt 10, and it is secured in its desired position by securing bolt 9, which passes through support adjusting slot 19. The doctor blade holder assembly 3 is connected through yoke 5 to the tensioning adjusting rod 6 by yoke pin 11. Tension adjusting rod 6 passes through tension resisting bar 7 at tension bar slot 20 (see FIGURE 3), and this bar is attached to dryer frame 13 by bolt 22 through bolt slot 21. Blade angle and tension adjusting hand wheel 8 screws onto tension adjusting rod 6, which is threaded about A of the way. Lock nut 16 secures this arrangement in the selected position.

The numbered items thus far have had reference to the parts shown; however, there are left side and right side items involved. The left side shown in FIGURE 2 must be complemented by a right side arrangement, parts of which must of necessity be the mirror image in design in order to provide the adequate support for the doctor blade assembly.

FIGURE 5 shows the details of a holder adjusting support. This is a particularly significant part of the apparatus because it was designed such that the line of contact between the doctor blade and drum surface remains stationary, relative to a fixed coordinate system, when angle a is varied. The particular part shown in FIGURE 5 is a right hand holder adjusting support. There also is a left hand holder adjusting support; however, in fabricating these parts there would be no difference in machining these pieces other than the marking along the radial surface 33. The markings shown in FIGURE 4A, i.e., 30, 40, 50, etc., are angles utilized in experimentation. In practice these could be replaced by any designation, such as letters or numbers, or simply fine lines. For the particular drum dryer used in this experimental work, the 30 through figures shown in FIGURE 4A are equivalent to at angles of 148 through 88 respectively when a doctor blade with a 15 'y angle is used.

For a satisfactory operation of the apparatus of the invention these three conditions must be taken into consideration (refer to FIGURES 2 and 4): (1) The holder adjusting support pivoting axis 32 must coincide with the preselected line 34, which is the location at which the film of food product 30 is to be removed from the drum surface by the doctor blade; (2) the radial distance between holder adjusiing support pivoting axis 32 and the doctor blade assembly pivoting axis 31 must be equal to the distance between the doctor blade assembly pivoting axis 31 and the doctor blade edge 12; and (3) center line 35 of support adjusting slot 19 must be a circular arc with a center of curvature coinciding with holder adjusting support pivoting axis 32 and a radius of curvature equal to the distance between line 34 and the center of securing bolt 9. The length of the centerline of slot 19 will depend upon the desired adjusting span.

The design of the holder adjusting support 4 is a crucial one in respect to the dryer drum arrangement which we have chosen for illustrating the reduction to practice of the method of the invention. Modifications in design must be made to correspond to the dryer drum system in which the method of the instant invention is to be employed.

In describing the invention we made reference to the various drawings. In so doing both the apparatus and the method of this invention can be shown.

In operation a change of angle or is accomplished as follows. First release bolts 9 on both the left and right supports 4L and 4R, and then turn blade angle adjusting wheels 8. Turning the hand Wheels will exert a force on yoke S by means of the adjusting rod 6 through yoke pins 11, thus causing the supports 4L and 4R to rotate on bolts 10 which act as the fulcrum until the desired angle etched on the periphery of the supports coincides with an index point (arrived at experimentally and annotated on the side frame 13). After this has been accomplished bolts 9 are secured and blade angle adjusting wheels 8 are further tightened clockwise to bring the doctor blade edge 12 to bear evenly on drum surface and exert the necessary pressure for properly scraping the dehydrated material.

The instant invention provides to the food processing industry a method and an apparatus for the drum drying of high sugar content foodstuffs, such as sweetpotatoes, peaches, pumpkin pie mix, pears, applies, apricots, plums, oranges, and the like wherein bulk density in the preparation of the dehydrated foodstuffs is controllable. The ability to control the bulk density is significantly functional in that the said bulk density can be adjusted without interrupting the continuous operation and immediate response is obtained. Bulk density is adjusted simply by the turning of knobs or wheels which in turn alter the angle which the doctor blade makes with tangent to the drum surface. Experience with the equipment to date dictates certain limits that are applicable to the pertinent angles. These perforce must be cited as limits to our invention; however, future experiment might yield valuable changes to the philosophies of the moment relative these angles. For the present we confine the limits of our angle a to be about from to 165, while angle 7 would be limited to about from 15 to The magitude limits of angle 13 would simply be dependent on the magnitude of the other two angles, and this measurement is of no significance whatever for purposes of the instant invention.

Although we have found many settings operable in the practice of our invention we prefer the initial settings of the doctor blade so that angle at would be between and and the use of a doctor blade which would have an angle 7 of about 15, which is a commercially acceptable angle in doctor blades. These initial settings allow an ample range of control to both increase or decrease angle oz as the drying operation warrants.

To reiterate, the present invention is mainly a method which would be very useful in the food processing industry, and can best be described as a method of regulating bulk density during drum drying of drum-dried foodstuffs of sugar content of at least about 25% by weight (dry-weight basis), wherein varying the impedance to the movement of the dried foodstuff across the beveled surface of the doctor blade is accomplished by varying the angle of attack about from 30 to which angle is formed by the intersection of two planes, one parallel to the beveled surface of the doctor blade and the other tangent to the drum surface at the point Where the doctor blade contacts the drum, wherein decreases or increases in bulk density of the drum-dried foodstuff are accomplished by increases or decreases in the magnitude of the pertinent angle; furthermore, the invention is also a mechanical improvement which can be applicable to existing equipment of the food processing industry. The improvement is a device which becomes part of the operating equipment in a drum dryer system. To reiterate, the present invention is also a device, in a drum dryer system, for controlling bulk density of high sugar content foodstuffs during processing wherein the said bulk density can be changed by changing the angle of attack a doctor blade makes with respect to the drying surface of a dryer drum.

We claim:

1. In a method of drum drying foodstuffs of high sugar content wherein the dried product is removed from a hot, rotating drum by a blade in transverse contact with said foodstuff while on the drum, the improvement which comprises maintaining optimum bulk density of the dried foodstuff by varying the angle of attack said blade makes with respect to the drum surface, thereby varying the impedance to the movement of dried foodstuff across the surface of said blade, decreasing the angle of attack to increase the impedance when an increased bulk density is desired, and increasing the angle of attack to decrease the impedance when a decreased bulk density is desired.

2. The method of claim 1 wherein the angle of attack varies about from 30 to 165.

References Cited UNITED STATES PATENTS 1,957,146 5/1934 Neubauer 159-11 2,352,220 6/1944 Overton 34120 XR 2,592,914 4/1952 Lavett 159-11 3,163,575 12/1964 No-bbe 15256.51 XR 3,228,454 l/1966 Kett 34110 XR FOREIGN PATENTS 74,364 5/1918 Austria.

FREDERICK L. MATTESON, JR., Primary Examiner H. B. RAMEY, Assistant Examiner US. Cl. X.R. 

